Left: Schematic view of the filament formation process due to compression of an overdensity by a shock wave (adapted from Inoue et al. 2018). The ambient B-field (indicated by the black lines) is parallel to the shock front. Right: Blow-up of the PV diagram (see figure 8) in ¹³CO(1–0) towards the filament YF for velocities between 6.8 km s⁻¹ and 9 km s⁻¹. The filament and the parent extended sheet-like structure are indicated with a white circle and a gray ellipse, respectively. The velocity gradients induced by the bending of the magnetic field are shown as converging arrows towards the filament (cf. subsection 4.2). (Color online)